This chapter explores the cultural dimension of interregional relations. It first defines regionalism, by a synchronic and diachronic comparison: “new regionalism” means the bottom-up, democratic, multilateral, post-hegemonic form that emerged in the 1990s. Second, the chapter draws attention to inter-regional relations, while proposing the concept of “hybrid interregionalism,” as the transnational relations between a regional organization such as the EU, on the one hand, and a large state, like China, on the other hand. Neither regionalism nor interregionalism are only about trade: they are multidimensional and structural features of increasingly multilayered global governance. Third, the chapter proposes the concept of “competitive regionalism” in order to cope with the recently emerging, top-down, authoritarian and hierarchical, anti-multilateral forms of regionalism. Finally, the chapter ponders how and to what extent the cultural dimension affects interregional relations, toward or versus a new multilateralism: are we moving from Eurocentric patterns of the past toward more even, balanced, multipurpose partnerships as an alternative to a civilization clash between irreconcilable and closed regions?